It has previously been proposed to manufacture industrial diamonds using a high pressure cylindrical vessel which is provided with an insulating liner. One such arrangement is shown in U.S. Pat. No. 4,118,161. In the arrangements shown in this prior patent, the insulating liner is disclosed as stopping short of the end of the cylindrical high pressure chamber where the movable piston is located. The space between the end of the liner and the piston is disclosed as including driver material made up of zinc and/or lead. When the piston is advanced into the high pressure chamber, the driver material is disclosed as going into the end of the insulating liner, so that the liner is not deformed. In the prior patent, an end heater element is disclosed for increasing the temperature near the end of the charge adjacent the movable piston, to compensate for the additional cooling which occurs adjacent the piston. The end heater element is apertured. In practice, when a structure such as that described hereinabove is employed, the end heater tends to tilt, and a portion of the charge flows out into the space around the end heater, and some of the driver material comes in contact with the charge area. This undesired result tends to neutralize the effect of the heater, leading to non-uniform temperature, and reduces the available yield of industrial diamonds which normally should be produced by the heating and compression of the charge.
Accordingly, a principal object of the present invention is to increase the reliability and the yield of industrial diamonds or other products from very high pressure high temperature piston arrangements of the type described hereinabove.